The present invention relates to a process for preparing hexafluoroacetone by contacting, in the liquid phase, hexafluorothioacetone dimer with a gaseous oxidant such as O.sub.2 in the presence of a catalytic amount of an alkali metal halide and an aprotic solvent such as dimethylformamide.
Hexafluoroacetone is a known compound useful as an intermediate in the preparation of hexafluoropropanol and hexafluoroisobutylene, and for the preparation of compounds containing the (CF.sub.3).sub.2 C-- group.
W. J. Middleton et al. (J. Org. Chem., 30, 1384-1390 (1965)) disclose preparation of hexafluoroacetone by gas phase oxidation of hexafluorothioacetone dimer with nitric oxide, NO, at 650.degree. C., over quartz in a Vycor tube. However, this reference reports that nitric oxide does not react with hexafluorothioacetone dimer at low temperature, and that oxygen, which is also unreactive at lower temperatures, reacts with hexafluorothioacetone dimer at 650.degree. C. to give only high conversion thereof into carbonyl fluoride and sulfur dioxide, but no hexafluoroacetone.
U.S. Pat. Nos. 3,164,637 and 3,257,457 (L. G. Anello et al.) disclose preparation of hexafluoroacetone by high temperature, gas phase fluorination of hexachloroacetone with HF in the presence of a chromium catalyst.
U.S. Pat. No. 4,057,584 (T. Touzuka et al.) discloses preparation of hexafluoroacetone by gas phase oxidation of perfluoropropene with oxygen over a fluorinated alumina catalyst.
These prior art preparations operate in the gas phase, employ high temperature, special equipment and specially treated catalysts.
In the presence of fluoride ion, hexafluorothioacetone dimer in dimethylformamide is in equilibrium with monomeric hexafluorothioacetone (T. Kitazume et al. Chemistry Letters, 267 (1973)).
Accordingly, there is a need for an economical process for the preparation of hexafluoroacetone which operates at convenient temperatures without special equipment or expensive catalysts.
It is an object of the present invention to provide a process for a liquid phase preparation of hexafluoroacetone at low temperature. This and other objects and advantages of the present invention will become obvious from the following description.